The seller is correct. Ebay wont get involved and have no facility to deal with matters like this.
However I note from your message this quote: "Instead, they are asking me to email them directly with my PayPal email address or username" - DO NOT give them both these details as they will have access then to your paypal account. They only need the EMAIL address. Re the other order details I would just forward the order number (if you have it)
To be honest I am very surprised that a seller is doing this after 5 years since you purchased an item.